With good performance, she could be the highest-paid woman on the FTSE, ousting Whitbread's Alison Brittain, whose pay could reach more than £6million with performance-related incentives, and Imperial Brand's Alison Cooper, who was paid £5.5million in 2016.

None of them come close to Bet365 chief executive Denise Coates, 49, who took home £117.5million last year.

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However, she runs a privately-owned company so is not part of the elite blue-chip index.

Glaxo, which faced pressure from shareholders to curb Walmsley's pay earlier this month, said Walmsley's maximum earnings are still around 25 per cent lower than Witty's and her pay package is more likely to fall to around the £3million mark.

Witty, who received £6.8million in 2016, had been entitled to a maximum pay package of up to £11.6million.

He is one of the most respected bosses in the FTSE 100 and has been chief executive since 2008.

Earlier this month it was reported that Urs Rohner, chair of Glaxo's remuneration committee, had suggested a package to grant Walmsley a base salary of just under £1m to reflect her experience level.

A spokesman for GSK said: 'We have been in active consultations with shareholders on these matters and have been over several months.

'Following feedback from shareholders we have adjusted the remuneration policy.'

Walmsley, who was unveiled as Witty's successor last September, is the first female boss of Glaxo, the third biggest company on the FTSE with a global workforce of more than 100,000.

Although she grew up in Kent, Walmsley was born in Barrow-in-Furness, Cumbria, into a naval family, and is the daughter of Vice-Admiral Sir Robert Walmsley, former chief of defence procurement at the Ministry of Defence.

She was educated at the £30,000-a-year St Swithun's boarding school in Winchester before studying classics and modern languages at Christ Church, Oxford. Joining Glaxo in 2010, she has run its consumer products unit.

Before taking the top job, Walmsley said she asked herself: 'How could a mum and a wife take on something so big?'

But she accepted after her husband David told her she would manage just fine. The couple live with their three sons and daughter in a £3.7million house in south-west London.